The invention relates to a two-way valved vascular catheter fabricated of extremely soft, flexible material and utilizing a removable internal pushing member abutting the closed proximal end to allow intravascular insertion. The two-way valve permits fluid to flow from the catheter if a predetermined pressure differential between inside and outside the catheter is exceeded but prevents flow in the opposite direction unless a second predetermined negative pressure differential is exceeded.
Our U.S. Pat. No. 4,327,722, entitled Method for Intravenous Therapy and Hyperalimentation, disclosed a flexible silicon rubber catheter which has a slit valve adjacent its closed proximal end. The term "proximal end" refers to the forward end of the catheter which is inserted into the patient's body. The term "distal end" refers to the rearward end thereof which is situated externally of a patient's body.
The valved catheter disclosed in such patent was designed for hyperalimentation, in which high concentrations of nutrients are infused into the venous system, as well as other instances in which therapeutic agents or the like are intravascularly administered. The catheter valve of such catheter was designed to prevent retrograde flow of blood into the proximal end of the catheter. When the hydrostatic pressure inside the catheter exceeds the pressure outside the catheter by a predetermined amount, the potential opening defined by the valve slit expands to allow fluid to flow undirectionally through and out of the catheter. When the pressure differential drops below this predetermined amount, the valve opening closes to prevent retrograde flow of blood into the catheter.
One prior art catheter having a slit defined one-way valve is the PUDENZ (trademark) atriocephalic catheter manufactured by Heyer-Schulte, Inc., a subsidiary of American Hospital Supply Export Corporation. This catheter of silicon rubber is specifically designed to drain ventricular fluid from the brain to the heart to relieve excess ventricular pressure. It is formed with a closed end and with four equiangularly positioned slits adjacent the end. Because of its design, fluid could flow only out of the slits. The valved end of the catheter is disposed within the right atrium of the heart, thus preventing the retrograde flow of blood from the heart into the cerebral ventricles. While this is the primary designed use of the PUDENZ atriocephalic catheter, it has also occasionally been used to infuse therapeutic fluids into the vascular system.
Another slit valved one-way catheter of silicon rubber, formerly marketed by the Extracorporeal Company, was used for intravascular infusion. The Extracorporeal catheter had a slit valve which, due primarily to the short slit length, was adapted only to permit fluid flow out of the catheter.
We realize that it would be desirable and advantageous to modify the valve of our previously disclosed closed ended intravascular infusion catheter so that retrograde flow from the blood vessel through the catheter valve would be possible under certain defined conditions. Such a valved catheter could not only be used to infuse fluids into the body but also to withdraw blood or other body fluids for analysis, to relieve excess pressure, as well as to permit confirmation of the catheter's position during insertion.
U.S. Pat. No. 3,885,561 to Cami discloses a closed ended catheter for the administration of epidural anesthesia. The illustrated catheter has a plurality of longitudinal slits through which fluid can escape from the catheter but through which body fluid can be drawn, it is stated, upon the application of negative pressure in the catheter. So that the catheter wall will not collapse, the slits are longitudinally and circumferentially offset from one another so that no single diametral plane has more than one slit and the dihedral angle between the diametral planes carrying adjacent slits is at least 45.degree..
Notwithstanding the possible utility of such a catheter for the administration of epidural anesthesia, its use in other areas of medical therapy, and specifically in the area of extended intravascular therapy and access, is associated with several serious drawbacks.
First, the Cami catheter is fabricated of a thermoplastic material, and it must be of sufficient rigidity and stiffness that it can be easily advanced through an introducing needle and into the tissues without bending or kinking which would obstruct the flow of anesthetic fluid through the catheter or resist withdrawal of fluid from the catheter.
The use of stiff, thermoplastic material is disadvantageous for catheters adapted for extended intravascular implantation. A stiff catheter will not conform to the curvature of vessels and thus will impinge on the luminal surface of vessels into which it is placed, especially at points of curvature, causing irritation and erosion of the vessel lining endothelium. This reaction, in blood vessels, will lead to inflammation of the endothelium with an increased tendency for local clot formation and thrombosis. An additional disadvantage is that with a stiff, nonstretchable catheter, relative motion between the skin insertion site and the point of catheter attachment to the skin such as occurs during repeated movement, for example, during respiration or voluntary muscular movement of the arm or hand, will cause the catheter slightly to move in and out through the epidermal penetration site and thus introduce bacteria on the skin surface into the insertion wound and along the catheter surface. This may result in infection at the insertion site which may extend along the catheter into the vessel in which the catheter is implanted. Septicemia may result. A further disadvantage is that the stiff catheter material may kink to obstruct flow of therapeutic fluid therethrough or impair withdrawal of body fluids. This is especially likely if the catheter is placed across a joint space, where repeated flexion and extension occurs. Thus, such catheter is restricted in its anatomical areas of usage.
It will be appreciated that the disadvantages of a stiff, thermoplastic fabrication material are of much greater medical consequence if the catheter must be in place and maintain function without complications for days, weeks, months, or even years as is the case for intravascular catheters.
Moreover, a catheter of a thin, relatively stiff plastic material is subject to fracture contiguous the valve opening upon repeated cycles of valve opening.
Another serious drawback of a valved catheter of stiff material is the damage caused to cellular elements which are injected into the body or withdrawn from the body through the valves of the catheter. With a stiff thermoplastic material, significant pressure differential between inside and outside the catheter is necessary to cause the valve to open in either direction. The cellular elements such as erythrocytes, leukocytes, or platelets which are infused through the catheter valve are subjected to forces and pressure differentials which may damage or destroy them. This would cause hemolysis of erythrocytes and functional damage to other cellular elements such that after forcible injection they no longer maintain their normal function. This could be an even greater problem when body fluids containing cellular elements are withdrawn through a valve in a stiff catheter. Because significant negative pressure must be applied to cause the valve to open, cells drawn through the valve are subjected to a dramatic pressure change which could result in cell rupture and damage. Chemical or hematologic analysis performed on body fluid withdrawn through such a valve may not be accurate due to such damage, and errors in subsequent patient therapy would result.
Yet another disadvantage of a slit valve in the wall of a stiff catheter is that the valve surfaces, being fabricated of a stiff plastic material, will tend to lose their ability to form absolutely tight seals after several cycles of usage. That is, each cycle of deformity inward and outward causes the stiff, inelastic surfaces to move against each other and may result in permanent deformities in the surfaces, especially at the sharp internal and external edge of the valve surface. If such occur, they allow inadvertent retrograde flow into the catheter lumen with its attendant adverse effects of clot formation within the catheter, rendering it unusable, or possible retrograde hemorrhage through the catheter should it become distally disconnected.